The present invention relates to power control for wireless communication systems and, in particular, fast adaptive power control system and methods for a variable multirate communication system.
Various methods of power control for wireless communication systems are well known in the art. An example of an open loop power control transmitter system for a single rate data system is illustrated in FIG. 1. An example of a closed loop power control transmitter system for a single rate data is illustrated in FIG. 2.
The purpose of both systems is to rapidly vary transmitter power in the presence of a fading propagation channel and time-varying interference to minimize transmitter power while insuring that data is received at the remote end with acceptable quality. Typically, in a digital implementation, transmitter power is varied by applying a varying scale factor to the digital data, as opposed, for example, to varying the gain of an RF amplifier.
In state-of-the-art communication systems such as Third Generation Partnership Project (3GPP) Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems multiple channels of variable rate data are combined for transmission. FIGS. 3 and 4 represent prior art open and closed power control transmission systems, respectively. Background specification data for such systems are found at 3GPP TS 25.223 v3.3.0, 3GPP TS 25.222 v3.2.0, 3GPP TS 25.224 v3.6 and Volume 3 specifications of Air-Interface for 3G Multiple System Version 1.0, Revision 1.0 by the Association of Radio Industries Businesses (ARIB).
Such open and closed loop power control systems for variable multirate wireless communications systems respond relatively slowly to data rate changes, resulting in sub-optimal performance such as relating to excessive transmitter power and below-quality received signals. It would be desirable to provide a fast method and system of power control adaption for data rate changes resulting in more optimal performance.
The invention provides a method of controlling transmitter power in a wireless communication system in which user data is processed as a multirate signal having a rate N(t) and in which the user data signal having rate N(t) is converted into a transmission data signal having a faster rate M(t) for transmission. The transmission power is adjusted on a relatively slow basis based on quality of data received by a receiver of the transmitted data. The transmitter power is determined as a function of N(t)/M(t) such that a change in the data rate in the user data signal or the rate of the transmission data signal is compensated for in advance of a quality of data based adjustment associated with such data rate change. Preferably, the user data signal having rate N(t) is converted into the transmission data signal having the faster rate M(t) by repeating selected data bits whereby the energy per bit to noise spectrum density ratio is increased in the transmission data signal.
The method is applicable in either an open or closed power control system where a scale factor is applied to control transmitter power. In implementing the invention in a transmitter of either an open or closed system, preferably (N(t)/M(t)) is applied to the scale factor.
The method is applicable to an open loop power control system where the transmitter receives a reference signal, reference signal power data, measured interference power data, and target signal to interference ratio (SIR) data which SIR data is based on relatively slowly collected received signal quality data. The transmitter measures the reference signal to determine received reference signal power and computes a path loss based on the received reference signal power data and the determined reference signal power. The transmitter then computes the scale factor based on the computed path loss, the received measured interference power data, the target SIR data and (N(t)/M(t)).
The method is also applicable to a closed loop system where the transmitter utilizes step up/down data generated by the receiver and computes the scale factor based on the step up/step down data and (N(t)/M(t)). Preferably, the step up/down data is generated by the receiver by combining measured interference power data of the signal received from the transmitter with target signal to interference ratio (SIR) data based at least in part on relatively slowly collected received signal quality data. The target SIR data is preferably computed by multiplying a nominal target SIR data based on relatively slowly collected received signal quality data by a factor N(t)/M(t) so that the target SIR data is quickly adjusted when a change in data rate occurs.
The invention also provides a transmitter for a wireless communication system in which user data is processed as a multirate signal having a rate N(t) and in which the user data signal having rate N(t) is converted into a transmission data signal having a faster rate M(t) for transmission. The transmitter transmission power is adjusted on a relatively slow basis by applying a scale factor to the transmitter power based on quality of data received by a receiver of the transmitted data. The transmitter includes a data signal rate converter which increases the user data signal rate N(t) to a higher data transmission rate M(t) and a processor for computing a transmission power scale factor based in part on data generated by the receiver related to quality of data received. The data signal rate converter is associated with the processor such that the processor computes the transmission power scale factor as a function of N(t)/M(t) whereby a change in the data rate in the user data signal or the rate of the transmission data signal is compensated for in advance of a receiver quality of data based adjustment associated with such data rate change.
Preferably, the data signal rate converter converts the user data signal having rate N(t) into the transmission data signal having the faster rate M(t) by repeating selected data bits whereby the energy per bit to noise spectrum density ratio is increased in the transmission data signal.
The transmitter is configurable as part of an open loop power control system where the transmitter receives from the receiver of the transmitted data: a reference signal, reference signal power data, measured interference power data, and target signal to interference ratio (SIR) data which SIR data is based on relatively slowly collected received signal quality data. As such, the transmitter includes a signal measuring device which measures received reference signal power and path loss processing circuitry for computing a path loss based on the received reference signal power data and the measured received reference signal power. The transmitter processor computes the transmission power scale factor based on the computed path loss, the received measured interference power data, the target SIR data and (N(t)/M(t)).
The transmitter is also configurable as part of a closed loop power control system where the transmitter receives step up/down data from the receiver of the transmitted data. As such, the transmitter processor computes the transmission power scale factor based on the received step up/step down data and (N(t)/M(t)).
Other objects and advantages will be apparent to those of ordinary skill in the art based upon the following description of presently preferred embodiments of the invention.